Chapter 5: Rate Law Analysis of Water Splitting Photoelectrodes

In this chapter, we discuss how rate law analyses can shed light into the kinetics and reaction mechanisms of those processes involved in the production of solar fuels. We show that the key data necessary to elucidate rate laws can be easily obtained by combining photo-induced absorbance (PIA) and transient photocurrent (TPC) measurements. The chapter is structured as follows: in the first part, we give a theoretical background (Section 5.1.1) on the use of rate laws and introduce our methodology and experimental approach (Section 5.1.2). In the second part, we show the potential of this technique through several practical examples on state-of-the art systems which cover: oxygen evolution, on α-Fe₂O₃ (Section 5.2.1.1) and BiVO₄ (Sections 5.2.1.2 and 5.2.1.3) as well as proton reduction on a multi-layer photocathode, Cu₂O/AZO/TiO₂/RuO_x (Section 5.2.2). In addition, the role of the catalyst is also discussed in detail in the last two sections. The kinetic analysis of these systems demonstrates that our methodology is capable of yielding reaction orders and rate constants, both key experimental parameters needed to advance the rational design of photoelectrodes for solar fuels production.